1. Field of the Invention
This invention relates to display systems and, more particularly, to a system for reading and writing text characters in a color graphics raster scan, all points addressable video display.
2. Discussion of the Prior Art
A video display typically provides an interface between a data processing machine and a user. Generally, a video image may comprise either strings of characters or of graphics, each of which requires different storage and, heretofore, processing requirements. Because of these differing requirements, many prior art video display systems do not permit the combining of text and graphic data on the same screen. However, many applications of graphic displays would be greatly enhanced by the provision of character data, such as legends on charts or graphs.
U.S. Pat. No. 4,149,145 describes a video display permitting the placement of character data within the region of display of graphic information. This is done by combining both graphic and character data in a video register. Each of the graphic and character data are separately developed, with a character generator providing the character image components and a graphic generator providing the graphic image components. These two components are merged or superimposed to provide a composite video signal. However, in the system of U.S. Pat. No. 4,149,145, there is no provision for reading text characters from the composite signal, and unnecesary complexity is required by the use of separate text character and graphics generators.